1. Technical Field
The present invention relates to valve seat inserts for internal combustion engines and methods of making the same, and more specifically, to valve seat inserts that are precision formed and surface treated prior to insertion into internal combustion engines.
2. Related Prior Art
Valve seat inserts produced by known monolithic or composite methods may suffer wear in certain engine applications or they may cause wear of other engine parts such as the mating valve. In using monolithic or composite valve seat inserts, it is necessary to finish machine the seating surface after insertion into the cylinder head or engine block. In order to do this finish machining, the material employed in the insert must have some amount of machinability, which, in turn, may compromise the material's wear resistance.
When using monolithic material, it is normal practice to produce valve seat inserts out of the monolithic material via casting, wrought, or powder metallurgy practices. The valve seat inserts are then inserted into the cylinder head or engine block, and the seating surface is machined. The wear resistance of the insert's seating surface is thus the same as the bulk monolith from which the insert has been made, and is generally susceptible to wear problems.
Composite type inserts have also been used, with either a weld overlay or a bimetallic power metallurgy product, with a wear resistant material applied over a lower alloy substrate. However, the valve seat is first inserted into the cylinder head or engine block, and the seating surface is then finish machined after insertion. This finish machining after the wear resistant material has been applied compromises the resistant material, and makes the valve seat insert more susceptible to wear.